Faecal composting

– how to build and maintain a compost for faeces from dry

urine diverting toilets

Ebba af Petersens Barbro Beck-Friis WRS Uppsala AB

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Content

Content ........................................................................................................................................ 2

Introduction ................................................................................................................................. 2

Urine diverting dry toilets ....................................................................................................... 3

Nutrient content in urine and faeces ....................................................................................... 3

Use of urine ............................................................................................................................. 3

Collection of dry faeces .......................................................................................................... 4

Faecal composting ....................................................................................................................... 4

Why composting? ................................................................................................................... 5

Composting process ................................................................................................................ 5

Sanitation ................................................................................................................................ 6

Compost container ....................................................................................................................... 6

Measures and material ............................................................................................................ 7

Location of compost ............................................................................................................... 7

Build your own compost container ......................................................................................... 7

Maintenance ................................................................................................................................ 9

How to start the composting? ................................................................................................. 9

How to run your compost? ...................................................................................................... 9

Composting period ................................................................................................................ 10

After composting ....................................................................................................................... 10

Handling of compost soil ...................................................................................................... 10

Use as fertilizer on edible and non-edible crops ................................................................... 11

FAQ (Frequently asked questions) ............................................................................................ 11

References: ................................................................................................................................ 12

This publication has been produced with the financial assistance of Sida and the

European Commission. The views herein shall not necessarily be taken to reflect the

official opinion of Sida or the European Commission.

Introduction

Sanitation of toilet waste is one of the most important health factors. A

sustainable sanitation toilet system means a system that prevents disease

and promotes health, protects the environment and conserves water, and

recycles nutrients and organic matter. The main challenge is to develop

sustainable sanitation systems which give effective pathogen removal.

One person leaves about 60 litres human excreta and toilet paper per

year, which corresponds to a nutrient amount of 0,55 kg nitrogen (N) and

0,18 kg phosphorus (P). Around the Baltic Sea live about 20 million

people with on-site sanitation for single family households or with no

treatment at all.

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Urine diverting dry toilets

Urine diverting toilets with dry

handling of faeces are often a cost-

efficient, hygienic and environ-

mentally friendly alternative to

water closets. Urine diverting dry

toilets also facilitates recovery of

plant nutrients present in toilet

waste. After storage, urine can be

used as fertiliser. Faeces can be

used as fertiliser and soil condi-

tioner after composting. This

handbook describes mainly how

the composting of faeces is done.

Figure 1.Example of a urine diverting

dry toilet in porcelain.

Nutrient content in urine and faeces

Most of the nitrogen and about 2/3 of the phosphorous in the toilet waste

is present in the urine, see table below. The concentrations in human

urine from urine-diverting toilets, including some flush water, is similar

to that of cow manure, about 3 g N/l urine and 0,2 g P/l urine. Urine is a

good nitrogen fertiliser, with similar effects as chemical fertilisers, and

should be used for leafy vegetables and other nitrogen demanding plants.

Table 1. Nutrient content in urine and faeces.1

Fraction Amount

(kg/person,

year)

N

(kg/person,

year)

P

(kg/person,

year)

K

(kg/person,

year)

Urine 550 4 0,37 1

Faeces +

toiletpaper

60 0,55 0,18 0,36

Total 610 4,55 0,55 1,36

The faecal fraction has a lower nutrient content than urine, and has also a

lower plant availability, as the nutrients mainly are organically bound and

therefore latent. The organic matter can contribute to the soil by e.g.

improving soil structure and increasing water holding capacity.

Use of urine

Before using the urine from a public toilet or a larger system of toilets, as

a fertiliser, it needs to be hygienically safe. This is done by storage for a

certain period of time, see table below. If the collected urine is coming

from a family and will be used in their own garden, storage is not needed.

The urine should be applied to the plants during the growing season,

when the plants can use the nutrients, and not during late autumn or win-

ter.

1 Jönsson et al. Guidelines of the use of urine and faeces in crop production. EcoSanRes

Report 2004-2.

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Table 2. Recommended storage times for urine mixturea based on estimated

pathogen contentb and recommended crops for larger systemsc

Storage temperature

Storage period

Possible pathogens in the urine mixture after storage

Recommended crops

4 °C 1 month Viruses, protozoa Food and fodder crops that are to be processed

4 °C 6 months Viruses Food crops that are to be processed, fodder cropsd

20 °C 1 month Viruses Food crops that are to be processed, fodder cropsd

20 °C 6 months Probably none All cropse

a) Urine or urine and water. When diluted, it is assumed that the urine mixture has a pH of at least 8.8 and a nitrogen concentration of at least 1 g/l.

b) Gram-positive bacteria and spore-forming bacteria are not included in the underlying risk assessments, but are not normally recognized as a cause of any infections of concern.

c) A larger system in this case is a system where the urine mixture is used to fertilize crops that will be consumed by individuals other than members of the household from whom the urine was collected.

d) Not grasslands for production of fodder. e) For food crops that are consumed raw, it is recommended that the urine be applied

at least one month before harvesting and that it be incorporated into the ground if the edible parts grow above the soil surface.

(Table from WHO guidelines for the safe use of wastewater, excreta and greywater. Volume 1.)

Collection of dry faeces

Before starting to use the urine

diverting dry toilet, cover the bot-

tom of the collection container

with litter material. A biodegrada-

ble bag, e.g. paper bag, can also be

used for easier handling and to

keep the collection container clean.

Depending on how often the toilet

is used, and the size of collection

container, the interval of emptying

the faecal container varies. It is

recommended to empty at least

once a month in a household, to

make the procedure smooth.

Figure 2. Useful barrow for easy

transport of faeces to the compost

Faecal composting

Before starting to compost your faecal material, contact the local authori-

ties to check if a registration or permission is needed.

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Why composting?

By composting the faecal material from the toilet, pathogens are killed

and the material is safe to use as a soil conditioner in the garden for e.g.

berry bushes, trees and flowers. Moreover the material is reduced in vol-

ume and weight, have no odour, and can be manageable.

Composting process

Composting is a degradable process where the temperature increases in

the organic material. Temperatures above 50 oC are needed to sanitise the

material. However, faecal composting based entirely on faeces is often

not enough to achieve high temperatures. Co-composting faeces with

organic food waste can enhance the temperature development and its

stability and may be necessary when faeces have been collected during a

long period. But even if the temperature is not increased some sanitisa-

tion occurs. The high microbial activity kills many pathogens even if the

temperature is low but the result is of course a less safe compost product.

Since it is difficult to ensure that the temperature has risen above 50 oC in

the whole volume, a long composting/storage period is generally recom-

mended.

Composting is an auto-heated, aerobic decomposition process. Organic

matter is partially oxidized and through biological and chemical process-

es converted to residues with increased resistance to biodegradation. As a

result, heat and water are evolved together with a variety of gaseous

Figure 3. Typical temperature development during composting showing the

mesophilic (A), thermophilic (B) and cooling (C) phases.

products such as carbon dioxide and ammonia. The process involves mi-

crobial succession characterized by a mesophilic phase (25- 45oC) and a

thermophilic phase (45-80oC). Thereafter composting is characterised by

a cooling phase (Fig. 2). Composting is run by microorganisms and

therefore the process is basically dependent on air, water and nutrient

supply.

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Sanitation

Pathogens are inactivated in the environment over time depending on a

combination of factors such as moisture, temperature, pH, carbon content

and nutrient availability. Microbial competition for nutrients and antago-

nistic behaviour may also contribute to the reduction of pathogenic mi-

croorganisms. To assure a hygienic compost product, the temperature

increase is very important. Almost all pathogens are killed above 50oC.

The compost material must reach 50oC during one week. To be sure all

organic material is safety treated, the compost heap has to be turned care-

fully three times during this week. To be able to reach a high tempera-

ture the heap has to be big enough to create heat and the compost box

efficiently insulated and ventilated. The temperature increase is favoured

by adding organic household waste, called co-composting.

If 50°C is not reached during one week the process is regarded as stor-

age, and the human excreta needs a long storage period to be safe. This

means at least one year before the material can be used in the garden as

soil improver. Long storage is not as safe as composting and the sanita-

tion process is uncontrolled.

Compost container

A compost batch must rest for at least one year which means two con-

tainers are needed for acceptable handling. There a several human excre-

ta compost containers on the market. A compost container should fulfil

the following construction demands:

Two containers, separated from each other

Water tight floor

Tight-fitting lid

Good ventilation

Protected from birds, rats or insects (insect nets)

Robust

Figure 4. Prefabricated compost con-

tainer.

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Measures and material

The required size of the compost containers is dependent on how much

the toilet is used. Below is a table with volumes needed for summer

houses and permanent-living.

Table 3. Recommended compost volumes* for one family-households.

Summer houses Permanent houses

Latrine composting

Two containers taking 350 liters each

Latrine composting

Two containers taking 680 liters each or

three containers taking 500 liters each

Co-composting

Two containers taking 500 liters each

Co-composting

Two containers taking 750 liters each or

three containers taking 500 liters each

*When calculating on the volume, the inner volume of the container should be used.

The container can be made of wood, plastic or other robust material. If

wood is used, it must be free from toxic wood impregnation chemicals,

such as arsenic.

Location of compost

When choosing the place of your compost, the following aspects should

be considered:

Placed above the ground in the garden

The place should not be covered with water at any point during

the year

The place should be warm and wind protected, rather in shade

than in direct sunlight

At close distance to the toilet

Easy to reach also during winter time

Not too close to neighbours (>5 m) without asking them

No closer than about 20 m from a water supply, e.g. a groundwa-

ter well

Build your own compost container

By building your own compost containers you can reduce the costs and

adapt the system to local conditions in your garden. The compost can be

built in wood, and it can be built with prefabricated parts. If using planks

the following standard measures can be used:

Planks e.g. 21 x 120 mm

Crossbars e.g. 45 x 95 mm

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Figure 5. Example of a simple design for a faecal compost.

The size required is dependent on how much the toilet is used, see

Measures and material above. Below are examples of minimum

measures for two different sizes of compost.

350 liters Cylinder (cm) 70 in diameter, 90 height

(one chamber) Square(cm) 60 length*60 width*100 height

500 liters Cylinder (cm) 80 in diameter, 100 height

(one chamber) Square (cm) 70 length*70 width*100 height

A water tight floor is needed to avoid pathogens from the compost

reaching the ground by leaching. The most permanent, e.g. for a bigger

compost, is to build the floor in concrete. A simpler solution is to line the

floor with a thick plastic sheet. Either way, the water tight lining should

cover about 20 cm up on the walls.

The lid should be tight fitting and rodent safe to stop rats and birds from

getting in. The lid can be made of planks of a smaller dimension than the

rest of the container or in a lighter material, to make it easier to lift.

To facilitate emptying of the compost container, the front wall can be

fastened to the other walls by hasps, or wing nuts. In that way the wall

can easily be detached and the composted material can be removed with

little effort.

The compost container should be ventilated, to enable air to enter to the

compost material. If the container is built with planks, the slots between

the planks will be enough to aerate the compost. Ventilation holes can

also be drilled into the walls. If the holes or slots are too wide, they

should be covered by a net, to prevent rats or birds to enter.

A simple way to build a compost is to screw together four pre-fabricated

duckboards (e.g. 80*80 cm) from the building store, put a thick plastic

sheet on the bottom, cover the container with net and isolate it during the

cold months.

Water tight floor with lining 20 cm up on the walls, e.g. in concrete.

Tight fitting lid.

Ventilation

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Another example is taking a plastic

cylindrical container with a lid, drill

small ventilation holes in the upper

half, and start using it! To mix and

oxygenate the material, the barrel can

be tipped over and rolled a few turns.

Just make sure the lid is fastened.

When the first barrel is full, put it

aside to rest and start with a new one.

Figure 6. Plastic barrels are used

for different liquids. Used barrels

can often be bought cheaply.

Maintenance

How to start the composting?

Start with covering the container bottom with at least 10 cm of peat moss

or similar litter material. The peat helps to avoid leaching and ventilation.

Fill with faeces and toilet papers. For better composting mix the faeces

with dry and energy rich organic material. Co-composting with organic

food waste is improving the compost process.

How to run your compost?

The faecal matter has a water content of about 80 %, ideal compost con-

dition is 50-60 % water content. The compost must be mixed up with

drier material, see examples of adding materials in table 4. The adding

material volume can be about a third of the faecal matter volume. The

right water content is when the compost material is moist, but not so wet

that it is leaching.

The faecal matter has low carbon content and the compost needs extra

energy rich material for efficient degradation. Many of the suggested

adding materials are both dry and energy rich (table 4).

Figure 7. Good increase in temperature is achieved when faecal

matter and food waste is co-composted with old compost, straw

or chopped twigs.

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To avoid the compost material becoming a compact mass, a structure

material is needed. Mixing in chopped twigs, straw or sawdust is excel-

lent for obtaining a porous material where air can enter.

Table 4. Examples of adding material and their functions in a compost

Adding material Dry materi-

al

Energy rich

material (car-

bon rich)

Structure ma-

terial

Old compost x

Paper x x

Grass cut x

Straw x x x

Food waste x

Saw dust x x x

Chopped twigs x

Peat x x

To spread the material evenly in

the compost, and to get a better

oxygenation of the compost, the

compost can to be turned a few

times during the compost period.

Turning can be done with a spade

or a manure fork. It is enough if

only the upper layer is turned.

Figure 8. A manure fork is useful for

turning the compost.

Composting period

When the container is filled to two thirds, it is full. If the faeces are wet

put extra litter material and to avoid flies put peat moss on the compost

top. The compost heap must rest (sanitise) at least one year without add-

ing new faeces, before use as soil improver. If needed for use in soil with

growing vegetables two years rest is needed. WHO guidelines for safe

use of excreta recommend 1,5-2 years of storage before use of faeces at

household and municipal levels.

After composting

Handling of compost soil

Use gloves and boots when handling the compost material, even after the

composting period. Wash your hands afterwards. It is important to cover

the compost material with soil directly after spreading to avoid contact

with people and animals.

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Use as fertilizer on edible and non-edible crops

Faecal compost has a lower nutrient value than urine, but still has a rather

high content of phosphorous (P) and potassium (K). The faecal compost

is valuable to crop production both for its fertilising effect and its effect

as a soil conditioner.

The mature compost product can be spread and used in the garden, for

example when establishing a lawn or in a flowerbed. It can also be used

when planting trees. Dig a hole, put compost in the bottom of the hole,

place the tree-plant, and cover with soil. This will stimulate the early

growth of the tree.

Recommended area is about 10 m2 per person and year for spreading the

composted faecal material (from permanent-living). It is important not to

over-fertilize, because of the risk of nutrient leaching.

If the compost soil is used for growing vegetables meant to be eaten

fresh, like carrots and lettuce, two growing seasons should pass between

spreading the compost and harvesting. This means that where compost is

spread autumn 2012, growing carrots can earliest be done 2014. For e.g.

potatoes, fruit trees and berry bushes, one growing season should pass

between application of composted material and harvest. Flowers and oth-

er plants not meant for human consumption need shorter time between

spreading of compost and harvest, so they can be fertilized with com-

posted faeces also during the growing season.

FAQ (Frequently asked questions)

How safe is faecal composting? After excretion, the concentration

of enteric pathogens usually declines with time by death or loss of

infectivity of a proportion of the organisms. Protozoa and viruses

are unable to grow in the environment outside the host, thus their

numbers will always decrease, whereas bacteria may multiply un-

der favorable environmental conditions. Helminths may need a la-

tency period after excretion before being infective. That means

faecal composting is not 100 % safe regarding infectious matters

and it’s important to use long sanitation time before growing vege-

tables on the compost. An efficient pathogen reduction need com-

post temperature over 50oC during one week with several turn-

ings.

Are there any chemical sanitation? Sanitation of faeces can be

achieved by mixing them with urea. Urea is degraded to ammonia

which is toxic to microbes. Adding ash and lime increase pH which

also means higher concentration of ammonia. This treatment need

to be performed in a closed container.

What is the best faecal mixture? To include kitchen waste is a good

way to optimize the compost process. Be aware of the fact that

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the volume of the containers must be bigger when extra waste is

included.

What are the environmental problems? Odour, flies and rats can

give problems. To avoid odour – have no standing water in the

compost. For less flies - put peat moss on the material to keep the

surface dry. Cover the container with a net to avoid rats.

Which litter material shall I use? Material that are dry and can

keep water like peat moss and chopped straw are good examples.

Must the two containers be similar? No, but about the same size. It

is good if both containers are insulated as the sanitation period is

at least one year before use.

References:

Avloppsguiden (2011) http://husagare.avloppsguiden.se/ta-hand-om-

urin-latrin-och-slam-på-din-egen-tomt.html.

Beck-Friis, B. (2001) Emissions of ammonia, nitrous oxide and methane

during composting of organic household waste. Doctoral thesis, SLU.

EcoSanRes (2004) Guidelines for the safe use of urine and faeces in eco-

logical sanitation systems. Report 2004-1.

EcoSanRes (2004) Guidelines on the use of urine and faeces in crop pro-

duction. Report 2004-2.

Jönsson, H., et al. (2005) Composition of urine, faeces, greywater and

biowaste for utilization in the URWARE model. In Urban water Rapport

Chalmers University of Technology.

Nordin, A. (2010). Ammonia sanitisation of human excreta. Doctotal

thesis, SLU.

Norrtälje kommun (2011) Eget omhändertagande av toalettavfall. Bygg-

och miljökontoret. www.norrtalje.se

WHO (2006) Guidelines for safe Safe Use of Wastewater, Excreta and

Greywater, vol 4. Geneva: World Health Organisation.

Vinnerås B., (2002) Possibilities for sustainable nutrient recycling by

faecal separation combined with urine diversion. Doctoral thesis, SLU.